Interpretive Summary: Consumers’ preference for less chemicals in the food supply has generated interest in natural antimicrobials for control of enteric pathogens in food. We evaluated the antimicrobial effect of lemongrass essential oil against Salmonella on organic fresh produce; namely, romaine and iceberg lettuce, and adult and baby spinach. Fresh produce leaves inoculated with Salmonella Newport were immersed in the lemongrass oil solution (0.1, 0.3, and 0.5%) for 1 or 2 min, and refrigerated. Surviving populations of Salmonella from produce samples stored for 3 days were determined by plating on selective medium. The antimicrobial activity of lemongrass oil against S. Newport was concentration and time dependent. Romaine, iceberg, adult spinach, and baby spinach samples showed between 10-to 100-fold reductions in S. Newport, respectively, when compared to the control (no oil). The antibacterial activity also increased with exposure time; iceberg samples treated for 2 min showed greater reductions than those samples only treated for 1 min. Further, antimicrobial efficacy of lemongrass oil increased with an increase in concentration. This study demonstrates the potential of lemongrass oil to reduce S. Newport on organic leafy greens. The information is useful to produce growers, consumer advocacy groups, and regulatory agencies.

Technical Abstract:
In an effort to discover new and natural antimicrobial treatments against Salmonella Newport on organic produce, we evaluated the antimicrobial effect of lemongrass essential oil on four different types of organic leafy greens inoculated with S. Newport. The effects of lemongrass treatment exposure time and how temperature abuse affects Salmonella survival were also investigated. The leafy greens tested included organic romaine and iceberg lettuces and organic adult and baby spinach. Each leaf sample was washed, dip inoculated with S. Newport (6 log CFU/ml) and air dried. Inoculated leaves were immersed in the lemongrass oil solution (0.1, 0.3, and 0.5%) for 1 or 2 min, and individually incubated at 4 or 8°C. Samples were taken at day 0, 1 and 3 for surviving populations of Salmonella. The antimicrobial activity of lemongrass oil against S. Newport was concentration and time dependent. Romaine, iceberg, adult spinach, and baby spinach samples showed between 0.6-1.5 log, 0.5-4.3 log, 0.5-2.5 log, and 0.5-2.2 log CFU/g reductions in S. Newport, respectively, when compared to the control (PBS) over the course of the experiment. The antibacterial activity also increased with exposure time; iceberg samples treated for 2 min showed significant reductions (P < 0.05) than those samples only treated for 1 min. Further, antimicrobial efficacy of lemongrass oil increased with an increase in concentration. The difference in recovery of Salmonella from fresh produce stored at abused temperature (8°C) and refrigeration temperature (4°C) was marginal. This study demonstrates the potential of lemongrass oil to reduce S. Newport on organic leafy greens.